Amplifier



May 26,1942. A. R. MORGAN I AMPLIFIER Filed Jan 25, 1941 Wi l:-

Patented May 26, 1942 zgsiosi AMPIJFIEE Adolph R. Morgan; Merchantyille,N. J., assignor to Radio Corporation of America, a'corporation ofDelaware Application January 25, 19 41,?Serial No. 375,893

9 Claims. (01. 119-171) This invention relates to an amplifier inwhich avoltage from a single source is amplified and converted intoa two-phaseor push-pull source.

. More particularly the' invention relates to a direct current amplifierfor amplifying and converting potentials from a single-endedscircuitinto pacitors are used to prevent undesired bias potentialsfrom beingapplied to the input circuits of. the push-pull amplifier which followsthe first amplifier. If these capacitors are eliminated, the biaspotentials applied to the input of the push-; pull amplifier wouldunbalance, and perhaps make inoperative, that amplifier. The unbalancedamplifier would not perform the desired function. I

One of the principal objects of the present invention is to providemeans whereby an amplifier and associated circuit may be used to amplifyand convert a single-phase current into an amplified current of twophases. Another object is to provide means for the amplification of adirect current whereby currents of equal magnitude and opposite sense,with respect to each other, may be obtained. A further object'is toprovide means in a direct current amplifier whereby currents from' a.siugle-ended" circuit may be amplified and converted into currentssuitable for application to apush-pull amplifier.

The invention will be described by referring to the accompanying drawingin which Figure 1 is a schematic circuit diagram of one embodiment ofthe invention; Figure 2 is a schematic circuit diagram of an embodimentof the invention in which a single-ended circuit maybe connected to apush-pull-amplifier provided with an alter- 'nating current outputcircuit; and Figure 31s a graph illustrating the operation of thecircuit.

Referring to Fig. 1, input terminals 1 and 3 are connected respectivelyto thegrid; of .an amplifier 5 arid to the groundejdmid-point 'I of apairof B batteries EBI and E32. The anode of of the amplifier 5is-connected through a resistor R2 to the negative terminal of thebattery EBZ.

The remaining. battery terminals are connected to ground as shown. Apotentiometer comprising resistors R3 and R4 is connected between thecathode of the amplifier and the positive terminal of the battery EBI. Asecond potentiometer comprising resistors R5 and R6 is connected betweenthe anode of the amplifier and the negative terminal of the battery E32.The movable contacts 9 andII', respectively, of the potentiometers' areconnected to output terminals I3, I5.- The output voltages EM and EH)appear between the output terminals I3 and I5, and .the intermediatebattery terminal or ground;

The preferred practical use of the device is an adjustment producing atruly push-pull output,

namely, one in which the amplified signals are equal in magnitude andopposite in phase. In this practical use of the device, the batteriesEBI and E132 are preferably of equal potential. The resistors RI. and R2are preferably of equal -value and the sum of these resistors RI and R2is chosen to representa suitable loading forthe amplifier 5. The sum ofthe resistances R3 and RI preferably equals the sum of the resistances.R5 and R6. Furthermore, the sum of theresistors R3 and R4 is preferablyof the order of 10 times RI. The final practical requirement isthat theratio of R3 to,R4 is equal to the ratio of R6. to R5 as will hereinafterbe explained.

Thooperation of the circuit is as follows: The currentthrough resistorsRI and R2 is the same.

Therefore; the voltage drop across RI will equalthe voltage drop acrossR2, since RI equals R2. If a-positive .potentia1 is applied to theterminal I, withrespect to terminal 3, the current through "theresistors RIland R2 will be increased over the value which'ismaintainedin the absence of an input signal. 'The increased current will beaccompanied by increased voltage drops-"across the resistors RI and R2.It follows that the volt the amplifier 5 is connected through aresistor-RI agesbetween the anode and ground and the voltages betweenthe cathodea'nd ground willchange ina push-pull manner as will thevoltages E211 and E217. B'y suitably adjusting the potentiometers theratio of R3 to R4 and R6 to R5 may bedetermined so that the voltagechanges in the output of the amplifier will be equal and opposite withrespect to each other. Furthermore, the

' quie sc ent or no signal output voltages for this adjustment, will beequal in magnitude and opposite in" polarity, It follows thatv thequiescent voltages can be adju'stedto any value between FBI (or E132)and the diiference in voltage bein supply potential.

tween E3! (or E32) and the drop across R or (R2).

By way of example, reference is made to Fi 3 with a zero input signalEl. The potentiometers may be adjusted so that nan. R4 R5 and EM willequal E217, and the steady voltage equals zero. Thus adjusted.thesloping lines in the graph represent the corresponding changes inoutput current as the input potential is made more negative or morepositive.

It is not intended that the adjustment of this circuit be limited totruly push-pull operation. Any number of combinations of Eta and E2b canbe obtained dependent on the adjustment of for the amplifier is not tobe limited to batteriesand that the power may be applied from a.suitable generator or rectifier and filter. In con--.

nection with power sources other than batteries.- itshould be evident tothose skilled in the art that this circuit (particularly the trulypush-pull adjustment) is relatively insensitive to changes Furthermore,any type of push-pull output amplifier may be used, as'ior example, thea-c amplifier of Fig. 2 in which the input potentials E211, EZb areapplied to the push-pull amplifiers l1 and I9, respectively. The outputcircuits of the push-pull amplifiers include a conventional outputtransformer 2|.

I claim as my invention:

1. An amplifier for ampliiying and converting a single steady currentinto currents of opposing characteristics including an amplifier havinggrid, anode, and cathode electrodes, 8. power source having endterminals and an intermediate -terminal, resistorsconnectingrespectively said and anode electrodes; a power source havinga.

positive terminal, a'negative terminal, and an intermediate terminal; apair of resistors connecting respectively said anode to said positiveterminal and said cathode to said negative terminal; means for applyingbetween said grid and said intermediate terminal the direct current tobe converted, a pair of potentiometers connected respectively betweensaid anode and said negative terminal and between said cathode and saidpositive terminal; and means connected respectively to each of saidpotentiometers for deriving 7 between said respective connecting meansand said intermediate terminal said direct currents of.

opposing characteristics.

3. An amplifier forconverting a direct current into two equal directcurrents of opposing characteristics including an amplifier having grid,cathode, and anode electrodes; a power source. having a positiveterminal, a negative terminal, and an intermediate terminal; a pair ofresistors of equal value connecting respectively said'anode to saidpositive terminal and said cathode to said negative terminal; means forapplying between said grid and said intermediate terminal the directcurrent to be converted, a pair of potentiometers connected respectivelybetween said anode and said negative terminal and between said cathodeand said positive terminal; and means connected respectively to each ofsaid potentiometers for deriving between said respective connectingmeans and said intermediate terminal said direct currents of opposingcharacteristics.

4. An amplifier for converting a direct current into two equal directcurrents of opposing characteristics including an amplifier having grid,cathode, and anode electrodes; a power source having a positiveterminal, a negative terminal, and an intermediate terminal; a pair ofresistors of equal value connecting respectively said anode to saidpositive terminal and said cathode to said negative terminal; means forapplying between said grid and said intermediate terminal the directcurrent to be converted, a pair of potentiometersconnected respectivelybetween said anode and said negative terminal and between said cathodeand said positive terminal; said potentiometers each having of the orderof ten times means connected respectively to each of said potentiometersfor deriving between said respecsaid anode and said negative terminaland be tween said cathode and 'said positive terminal,

tive connecting means and said intermediate terminal said directcurrents of opposing characteristics. I 5. An amplifier for converting asingle variable current into two currents which vary in opposite senseincluding an amplifier having grid, cathode and anode electrodes, apower source having positive and negative terminals and a center tap, apair of resistors of similar value connected respectively between saidpositive terminal and said anode and between. said negative terminal andsaid cathode, means for applying said single phase current to said gridand center tap,

output terminals for obtaining said currents be- 1 tween said center tapand voltage points intermediate said anode and said negative terminaland said cathode and said positive terminal, and means for adjustingsaid output terminals so that a predetermined current is obtainedbetween each of said output terminals :and said center tap.

6. An amplifier for converting a single variablecurrent into twocurrents which vary in opposite sense including an, amplifier havinggrid, 'cath- I ode and anode electrodes, 9. power source having positiveand negative terminals and a center tap,

a pair of resistors of similar value connected re-' spectively betweensaid positive terminal and said anode and between said negative terminaland said cathode, means for. applying said single phase current to saidgrid and center tap, a pair of potentiometers connected respectivelybetween and means ior adjusting said potentiometers so that saidcurrents are obtained between the adjustable contact of each of saidpotentiometers and said center tap. V 7. An amplifier for converting asingle variable current into two currentswhich vary in opposite senseincluding an amplifier having grid, cathode and anode electrodes, apower source having positive and negative terminals and a center tap, apair of resistors of similar value connected respectively between saidpositive terminal ,and said anode and between said negative terminal andsaid cathode, means for applying said single phase current to said gridand center tap, a pair of potentiometers connected respectively betweensaid' anode and said negative terminal and between said'cathode and saidpositive terminal, and means for adjusting said potentiometers so thatzero quiescent voltage with respect to said center tap is obtainedbetween the adjustable contact of each of said potentiometers and saidcenter tap and said two variable currents are obtained between saidcontacts and said center tap.

8. The combination of end and intermediate power'supply terminals, apair of direct current circuits including reversely arranged impedancesections connected-in parallel between said end terminals, means forsimilarly varying the current through one pair of the opposite endsections of said circuits, and means connected between said intermediateterminal and the other opposite end sections of said circuits forderiving'voltages displaced in phase from one another. i

, 9. The combination of end and intermediate power supply terminals, apair of direct current circuits including reversely arranged impedancesections connected in parallel between said end terminals, an electrondischarge device provided with an input circuit including saidintermediate terminal and with an output circuit including one pair ofthey opposite end sections of said circuits, and means connected betweensaid intermediate terminal and the other pair of the opposite endsections of said circuits for derivingvoltages displaced in phase.ADOLPH R. MORGAN.

